1. Field of the Invention
The present invention relates generally to reversed-phase liquid chromatography. More specifically, the present invention relates to a chemical composition used as a stationary phase in the reversed-phase liquid chromatography, a method for preparing the composition, a column used in the liquid chromatography, and a method for performing the liquid chromatography.
2. Description of Related Art
Reversed-phase liquid chromatography is the most popular separation method in liquid chromatography. More than 50 percent of all the applications in liquid chromatography are performed in reversed-phase mode. This popularity stems from a number of factors such as ease of use, rapid analysis time, and commercial availability of a large number of reversed-phase columns. Besides, the theory of reversed-phase liquid chromatography is also very well developed.
Early, many of the reversed-phase systems were developed using silica gel as the stationary phase matrix. However, conventional silica gel based packing materials have several disadvantages.
One disadvantage relates to the presence of acidic/active silanol groups. The presence of unreacted silanol groups lead to the adsorption of basic chemicals on the column, resulting sometimes in tailing peaks or complete disappearance. To alleviate this, the use of masking agents like alkylamine or the use of low pH mobile phases which would protonate the silanols became common practice.
Another disadvantage relates to pH stability. Conventional silica gel based packing materials have limited range of pH stability (2.5 to 7.5). At low pH, the silica-carbon bonds break down leading to the erosion of the bonded phase. At high pH, on the other hand, the silica gel itself dissolves, resulting in a loss of bonded phases. In both these instances, there is a change in the chromatographic profile. Recently, silica-based allys bonded phases which are stable to extended range of pH have been synthesized. Popular alkyl bonded phases are pentyl, octyl, and octadecyl bonded silica gels (respectively C5, C8, and C18) which are stable in the range of pH 1.5 to 10.0.
The separation power of liquid chromatography, on the other hand, can be attributed to the unlimited selectability of mobile phase conditions. The optimal utilization of the power of liquid chromatography requires development of new stationary phases. In this regard, another popular phase in reversed-phase liquid chromatography which has different and unique selectivities compared to the alkyl (C5, C8, and C18) bonded phases is phenyl phase (C.sub.n Ph). Certain phenyl bonded phases have been developed and their phenyl groups are generally bound with silica gel via zero to four methylene groups; i.e., n=0, 1, 2, 3, or 3 in (C.sub.n Ph) . However, these phases have limited pH stability and show poor retention capacity compared with the octyl (C8) and octadecyl (C18) bonded phases.
As a result, there is a need for a new phenyl bonded phase that has high pH stability at both extremes and improved retention capacity compared with the conventional alkyl bonded phases, hence better resolution.